We investigate displacive short-range order in pyrochlore ${\mathrm{Y}}_2{\mathrm{Nb}}_2{\mathrm{O}}_7$, which exhibits a nonmagnetic insulating state despite the presence of formally tetravalent ${\mathrm{Nb}}^{4+}$ ($S=1/2$) ions on the pyrochlore network. Synchrotron x-ray diffraction on a single crystal reveals a characteristic x-ray diffuse scattering (XDS) pattern primarily around $\mathit{q}=\{0.5,0.5,2\}$. Reverse Monte Carlo (RMC) simulations uncover local Nb displacements along the $⟨111⟩$ axes, leading to the formation of linear ${\mathrm{Nb}}_4$ tetramers. Our findings highlight a crucial role of molecular orbital degrees of freedom in stabilizing the nonmagnetic insulating state. This study demonstrates that RMC analysis of XDS provides a powerful approach for elucidating short-range correlations and the underlying mechanisms governing the physical properties of crystalline materials.

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• Disordered systems
• Transition metal oxides
• Monte Carlo methods
• X-ray diffraction
• X-ray diffuse scattering